This invention relates to methods to form electronic devices, such as capacitors, antifuses, transistor gate stacks, and these and other devices incorporating high K dielectric layer constructions.
As the density of DRAM cells increases, there is a continuing challenge to maintain sufficiently high storage capacitance despite decreasing cell area. Additionally, there is a continuing goal to further decrease cell area. One principal way of increasing cell capacitance is through cell structure techniques. Such techniques include three-dimensional cell capacitors, such as trenched or stacked capacitors. Yet as feature sizes continue to become smaller and smaller, development of improved materials for cell dielectrics as well as the cell design and structure become important. The feature size of higher density DRAMS, for example 256 Mb, will be on the order of 0.25 micron and less. Such overall reduction in cell size drives the thickness of the capacitor dielectric layer to smaller values, and conventional capacitor dielectric materials such as SiO2 and Si3N4 might become unsuitable. However it would be desirable to utilize silicon oxides and nitrides in spite of the reduced thicknesses due to the ease of use and available thorough understanding of how to integrate these materials in DRAM process flows. Yet processing associated with chemical vapor deposition of thin silicon nitride films in certain environments has also created other problems not directly associated with the capacitors.
For example, one prior art technique is the fabrication of stacked capacitors in a container shape within a borophosphosilicate glass layer (BPSG) to form the storage capacitors in DRAM circuitry. Here, a container opening is formed in a planarized layer of BPSG over a desired node location, typically in the form of a conductive polysilicon plug. The conductive electrode material is deposited to less than completely fill the opening, and then is typically chemical-mechanically polished back to provide a storage node electrode inside of the BPSG opening in the shape of a cup or container. Capacitor dielectric material is then provided over the storage node container, followed by deposition of a conductive cell plate layer which is subsequently patterned.
As circuitry integration and density increases, the corresponding dimensions and thicknesses of the various components also decreases. A typical capacitor dielectric layer in the above construction comprises a silicon dioxide/silicon nitride/silicon dioxide composite (ONO). The first oxide layer formed over the storage node electrode is typically native oxide formed by exposure of the exposed storage node material to ambient air. Silicon nitride is next chemical vapor deposited, for example utilizing a silicon hydride such as dichlorosilane and ammonia. Typical deposition conditions are at sub-Torr pressures and temperatures at or above 680xc2x0 C. more typically above 700xc2x0 C. The deposition process and the very thin nature of the typically deposited silicon nitride layer results in pin holes or other defects in the deposited layer. This is typically cured by a dense re-oxidation process which forms the outer silicon dioxide layer of the ONO construction. The prior art re-oxidation conditions for forming this outer oxide layer are conducted wet or dry at a temperature of from 800xc2x0 C. to 950xc2x0 C. at atmospheric pressure. for from 5 to 30 minutes. Subsequently, a conductive cell plate layer is deposited and patterned over the ONO dielectric layer(s).
However as the nitride thickness of the ONO construction over the storage node electrode fell to below 80 Angstroms, it was discovered that the underlying bulk silicon substrate was oxidizing to the point of circuit destruction. BPSG is known to be extremely diffusive to oxidizing components during the above-described re-oxidation conditions. Silicon nitride, on the other hand, is known to form a good barrier layer to diffusion of such oxidizing gases under such conditions. Yet, the silicon nitride deposited over the BPSG in conjunction with the capacitor dielectric layer formation was apparently inadequate in shielding oxidation of substrate material underlying the BPSG when the deposited silicon nitride layer thickness for the capacitors fell below 80 Angstroms.
The invention was principally motivated with respect to overcoming this problem to enable silicon nitride to continue to be utilized as a capacitor dielectric layer where its thickness fell to below 80 Angstroms in deposition also occurring over a doped oxide layer, such as BPSG.
The invention comprises methods of forming electronic devices, such as capacitors, antifuses, transistor gate constructions, and these and other devices incorporating high K dielectric layer constructions. In but one implementation, a first electrode and a doped oxide layer laterally proximate thereof are provided over a substrate. A silicon nitride layer is formed over both the doped oxide layer and the first electrode to a thickness of no greater than 80 Angstroms over at least the first electrode by low pressure chemical vapor deposition at a pressure of at least 1 Torr, a temperature of less than 700xc2x0 C. and using feed gases comprising a silicon hydride and ammonia. The substrate with silicon nitride layer is exposed to oxidizing conditions comprising at least 700xc2x0 C. to form a silicon dioxide layer over the silicon nitride layer, with the thickness of silicon nitride over the doped oxide layer being sufficient to shield oxidizable substrate material beneath the doped oxide layer from oxidizing during the exposing. A second electrode is formed over the silicon dioxide layer and the first electrode.
In one implementation, the doped oxide layer and first electrode are exposed to rapid thermal nitridation conditions effective to grow a seed nitride layer over at least the doped oxide layer to a thickness of at least about 8 Angstroms prior to chemical vapor depositing a silicon nitride layer. In another implementation, the substrate is exposed to a nitrogen containing atmosphere which is substantially void of silicon hydride at a temperature of at least about 850xc2x0 C. after chemical vapor depositing a silicon nitride layer.
In yet another implementation, a layer comprising. undoped oxide is formed over a layer of doped oxide. A first electrode is formed proximate the undoped oxide layer and the doped oxide layer. With the undoped oxide layer being outwardly exposed, a silicon nitride layer is formed on the undoped oxide layer and over the first electrode by low pressure chemical vapor deposition to a thickness of no greater than 80 Angstroms.
Other aspects and implementations are described below.